1. Field of the Invention
The present invention relates to an erbium-doped fiber amplifier and a wavelength division multiplexing optical transmission system equipped with the same, and more particularly to a cost-effective, wide-band, erbium-doped fiber amplifier and a wavelength division multiplexing optical transmission system equipped with the same.
2. Description of the Related Art
A conventional WDM (Wavelength Division Multiplexing) optical transmission system transmits optical signals of several wavelengths using one optical fiber. This allows for the efficient of transmission and transmitting the optical signals regardless of the transmission speed. WDM optical transmission systems are very useful for high-speed Internet networks that require large amounts of data to be transmitted. In order to meet of the high data transmission rate, the WDM optical transmission systems must have an expanded transmission bandwidth range. In this regard, a number of active research efforts are being made in conjunction with wide-band transmission systems for using both a C-band (Conventional band) and an L-band (Long band).
FIG. 1 shows a configuration of a conventional optical transmission system based on a 160 km SMF (Single Mode Fiber) using 80 channels with 10 Gbps capacity. As shown in FIG. 1, 40-channel optical signals for the C-band are modulated by a 10 Gbps modulator 111. The modulated signal is then dispersion-compensated by a DCF (Dispersion Compensated Fiber) 113. A C-band EDFA (Erbium-Doped Fiber Amplifier) 115 is used to amply the dispersion-compensated C-band optical signals. Forty-channel optical signals for the L-band are modulated by a 10 Gbps modulator 112. The modulated signal is then dispersion-compensated by a DCF 114. An L-band EDFA 116 is used to amply the dispersion-compensated L-band optical signals. The C-band optical signals have a wavelength in the range of 1530 nm-1560 nm, and the L-band optical signals have a wavelength in the range of 1570 nm-1610 nm.
In a transmission stage 110, the amplified C and L-band optical signals are combined to be transmitted within one optical fiber. The combined C and L-band optical signals are output from the transmission stage 110 and pass through an 80 km SMF 118. The combined C and L-band optical signals are then transmitted to an optical repeater 120. The optical repeater 120 separates the combined C and L-band optical signals into the C-band optical signals and the L-band optical signals band by band. The separated C-band optical signals from the optical repeater 120 are amplified by a second C-band EDFA 121 and then dispersion-compensated by a DCF 123. A third C-band EDFA 125 amplifies the dispersion-compensated C-band optical signals from the DCF 123.
The separated L-band optical signals from the optical repeater 120 are amplified by a second L-band EDFA 122 and then dispersion-compensated by a DCF 124 having a predetermined length. A third L-band EDFA 126 amplifies the dispersion-compensated L-band optical signals from the DCF 124. The amplified dispersion-compensated C and L-band optical signals are combined within one optical fiber, pass through the 80 km SMF 128, and reach a reception stage 130.
In the reception stage 130, the combined C and L-band optical signals are separated into the C-band optical signals and the L-band optical signals band by band. The separated C-band optical signals are amplified by a fourth C-band EDFA 132 and then de-multiplexed. The separated L-band optical signals are amplified by a fourth L-band EDFA 134 and then de-multiplexed.
As described above, the conventional optical transmission system needs to repeatedly perform the steps of separating combined C and L-band optical signals, dispersion-compensation, and amplification, respectively, in each of a transmission stage, e.g., in the optical repeater 120 and the reception stage 130. This is a significant shortcoming of conventional optical transmission systems because the number of optical devices such as amplifiers or dispersion compensating fibers is doubled and therefore the cost required for manufacturing the system increases.
Accordingly there is a need in the art for improved optical transmission systems that provide cost-effective solutions to this shortcoming of conventional optical transmission systems.